We consider pion interactions in an effective field theory of the narrow resonance X(3872), assuming it is a weakly bound molecule of the charm mesons D^{ 0} \bar D^{ *0} and D^{ *0} \bar D^{ 0}. Since the hyperfine splitting of the D^{ 0} and D^{ *0} is only 7 MeV greater than the neutral pion mass, pions can be produced near threshold and are non-relativistic. We show that pion exchange can be treated in perturbation theory and calculate the next-to-leading-order correction to the partial decay width \Gamma[X \to D^0 \bar D^{ 0} \pi^0].
Categories: hep-ph hep-ex nucl-th